1. Field of the Invention
The present invention generally relates to a network system for transmitting a signal using a plurality of channels, and a transmission method of the signal therein. More particularly, the present invention relates to a network system which transmits a signal through a plurality of channels and includes a node device for connecting a terminal equipment and the like to the plural channels and in which an interactive transmission is performed between the node devices.
2. Related Background Art
In recent years, study and development have been made with respect to network systems each of which employs a plurality of channels for transmission of a signal, since a high-speed network system, which includes terminal equipments connected thereto, is required, following an increase in speed of processing in each terminal equipment. As the plural channels, channels using different wavelengths are known, for example. As one of them, there has been proposed a multihop type in which transmitted data is relayed and transmitted in a node device interposed on the way from a signal transmitting terminal to a signal receiving or addressed terminal. Such a system is described in Biswanath Mukherjee, xe2x80x9cWDM-Based Local Lightwave Networks Part II: Multihop Systemsxe2x80x9d, IEEE Network July (1992), p. 20-32.
An object of the present invention is, therefore, is to provide a new network system which performs communication using a plurality of channels.
Prior to the description of the present invention, a reference example will be described to facilitate understanding of the present invention. The following reference example is based on the technology described in Japanese Patent Application No. 6-327496 filed Dec. 28, 1994, and Japanese Patent Application No. 7-325632 filed Dec. 14, 1995 as a Japanese domestic priority-claim declared application based on this Japanese Patent Application No. 6-327496.
FIG. 14, which consists of FIGS. 14A and 14B, illustrates a schematic diagram of a node device connected to a network system. The node device detects an optical signal at a predetermined wavelength which is transmitted on a ring-type wavelength division multiplexed transmission line, transmits a packet to its terminal equipment when the signal is the packet addressed to the terminal equipment connected to this node device concerned, and transmits other packets a packet from its terminal equipment to a next-stage node device by variable wavelength transmission means of a wavelength-circulating type which transmits signals at respective wavelengths. The node device of FIGS. 14A and 14B includes a control unit 149 which contains a buffer control unit 164 and a wavelength control unit 165. The buffer control unit 164 controls the read-out of buffers such that when a packet stored in buffers 141-148 is addressed to a sub-transmission line connected to an adjacent node device, the read-out of the packet stored in the buffer is not performed until a transmission wavelength of the variable wavelength transmission unit for transmitting the packet coincides with a reception wavelength of a fixed wavelength reception unit for outputting the packet to a separation-insertion unit connected to the addressed sub-transmission line in the adjacent node device. The wavelength control unit 165 controls the transmission wavelengths of variable wavelength transmission units in accordance with a pattern of a predetermined transmission wavelength control table which will be described later. An optical fiber 1401 is used as an optical wavelength multiplexed transmission line. The optical fiber 1401 serves as a transmission line between a coupler in an upstream adjacent node device and a divider in an adjacent node device on the downstream side. The power divider 1402 divides an optical signal transmitted on the optical fiber 1401 into eight portions and output them to eight fixed wavelength reception units.
The fixed wavelength reception units I 117, III 118, V 119 and VII 120 respectively include a fixed-wavelength filter and a photodiode and serve as fixed wavelength reception means. Similarly, the fixed wavelength reception units II 121, IV 122, VI 123 and VIII 124 respectively include a fixed-wavelength filter and a photodiode and serve as fixed wavelength reception means. The fixed wavelength reception units I to VIII each receive only a packet which is transmitted as one of optical signals having wavelengths xcex1 to xcex8. When the photodiode itself has characteristics that this is sensitive only to a predetermined wavelength, no fixed-wavelength filter is needed.
Separation-insertion units I 133, III 134, V 135 and VII 136 serve as separation-insertion means, each of which is operative to separate a packet, which is to be transmitted to a sub-transmission line, and a packet, which is to be transmitted to one of the buffer 145 to 148, out of a packet stream from each of the fixed wavelength reception units 117 to 120, while it is operative to add a packet from the sub-transmission line to the packet stream from the fixed wavelength reception unit 117 to 120 to the buffers 145 to 148. Similarly, separation-insertion units II 137, IV 138, VI 139 and VIII 140 serve as separation-insertion means.
Buffers II 141, IV 142, VI 143 and VIII 144 serve as buffer means to temporarily store the packets from the separation-insertion units 137 to 140 in memory regions corresponding to the respective transmission wavelengths of the variable wavelength transmission units. Similarly, buffers I 145, III 146, V 147 and VII 148 serve as buffer means.
Variable wavelength transmission units II 125, IV 126, VI 127 and VIII 128 are variable wavelength transmission means, such as tunable laser diodes (TLDs), which convert, under the control of the wavelength control unit 165, the packets from the buffers into optical signals each having a predetermined wavelength out of wavelengths xcex1 to xcex8 and send them through the coupler 1403 to the optical fiber 1404 used as the optical wavelength division multiplexed transmission line. Similarly, variable wavelength transmission units I 129, III 130, V 131 and VII 132 are variable wavelength transmission means, such as tunable laser diodes (TLDs).
In this reference example, the fixed wavelength reception unit I 117, the separation-insertion unit I 133, the buffer I 145 and the variable wavelength transmission unit I 129 constitute a set, and a packet received by the fixed wavelength reception unit I 117 is treated in this set but not in other sets. Similarly, the fixed wavelength reception unit II 121, the separation-insertion unit II 137, the buffer II 141 and the variable wavelength transmission unit II 125 constitute another set, and the other fixed wavelength reception units, the other separation-insertion units, the other buffers and the other variable wavelength transmission units respectively constitute other sets.
The coupler 1403 multiplexes the optical signals of wavelengths xcex1 to xcex8 which are sent from the eight variable wavelength transmission units, and supplies them to the optical fiber 1404.
The optical fiber 1404 serves as the transmission line between the coupler in this node device concerned and the divider in a downstream adjacent node device.
Sub-transmission lines I 1405 to VIII 1412 serve as packet transmission lines between the separation-insertion units and terminal equipments. The terminal equipments I 1413 to VIII 1420 are connected to the sub-transmission lines I to VIII, respectively. Each of the terminal equipments receives a packet output from each of the corresponding separation-insertion units, while it generates a packet to be transmitted to another terminal equipment and sends it through each of the sub-transmission lines to each of the separation-insertion units.
FIG. 3 is a block diagram of a network system in which five node devices of FIGS. 14A and 14B are connected by optical fibers. Node devices 301 to 305 shown in FIGS. 14A and 14B are respectively connected to eight terminal equipments through eight sub-transmission lines. Optical fibers 306 to 310 are each used as an optical wavelength multiplexed transmission line.
FIG. 4 shows the internal structure of each of buffers I to VIII which are utilized in this node device. The same internal structure is applied to all of the buffers I to VIII and the description will be made with respect to only one buffer.
In FIG. 4, a decoder 401 reads an address portion in a header section of a packet, which consists of this header section and a transmission data section, and determines whether or not a destination of the packet is the terminal equipment connected to an adjacent node device. If not, the decoder 401 instructs a demultiplexer 404 to set its output destination to a FIFO 406. On the other hand, if it is the sub-transmission line connected to the adjacent node device, the decoder 401 instructs the demultiplexer 404 to set its destination to a dual port memory 405, and at the same time instructs a writing address counter 402 to set a writing start address value of the memory region, into which the packet to be written.
A writing address counter 402 starts with the writing start address value, which is output from the decoder 401, and outputs discrimination signals of the memory regions, in which the packet is to be written, to a dual port memory 405 in due order. The memory region in the dual port memory 405, in which the packet is to be stored, is determined from a channel (a wavelength) connected to the terminal equipment to which the packet is addressed.
For example, when the packet is addressed to the terminal equipment II 1414 connected to the adjacent node device, the packet needs to be input, as an optical signal of a wavelength xcex2, into the fixed wavelength reception unit II 121 connected to the separation-insertion unit II 137 in the node device so that the packet can reach the terminal equipment II 1414, since the terminal equipment II 1414 is connected to the separation-insertion unit II 137 in the node device. In order to convert the packet into the optical signal of the wavelength xcex2, the packet needs to be stored into the memory region II in the dual port memory 405 corresponding to the wavelength xcex2, i.e., the memory region which stores the packet which is to be read from this buffer when the packet can be output at the wavelength xcex2.
Similarly, a reading address counter 403 starts with an offset value as a reading start address, which is output from the buffer control table, and outputs address signals for reading the packet from the dual port memory 405 in due order.
The demultiplexer 404 outputs the input packet to the dual port memory 405 or the FIFO 406 in accordance with instructions from the decoder 401. The dual port memory 405 is operative to perform reading and writing of the packet data independently.
Memory regions of the dual port memory 405, as shown in a memory map of FIG. 5, are established corresponding to variable wavelengths which can be modulated.
For example, the packet stored in the memory region IV is read only when the transmission wavelength of the variable wavelength transmission unit is set to the wavelength xcex4, and transmitted from the variable wavelength transmission unit as the optical signal of the wavelength xcex4. The packet stored in each memory region is converted into the optical signal of a wavelength corresponding to each memory region and output from the node device. A start of address in each of the memory regions I to VIII is A1, A2, A3, A4, A5, A6, A7 or A8.
The FIFO (First In First Out) 406 temporarily stores the packets input thereinto and outputs them to a selector in order of input. The selector 407 selects, in accordance with instructions from a reading control unit 609, either of outputs; one is from the dual port memory 405 and the other is from the FIFO 406, and outputs it to the variable wavelength transmission unit.
FIG. 6 shows the internal structure of the buffer control unit 164. In FIG. 6, buffer control tables I to VIII are read out in order in response to the address value which is output from a ROM counter 702 in the wavelength control unit 151. Then, predetermined offset values are respectively output to the reading address counters 403 in the buffers I to VIII. These tables are incorporated in a read-only memory (ROM). The contents of the buffer control tables I to VIII will be described later.
The reading control unit 609 counts clock signals which are output from the wavelength control unit, so that the reading control signal for reading the packet of the dual port memory 405 or the FIFO 406 can be output to the selector in each of the buffers I to VIII.
FIG. 7 shows the internal structure of the wavelength control unit 165. In FIG. 7, wavelength control tables I 703 to VIII 710 are read out in order in response to the address value which is output from the ROM counter 702. Then, predetermined wavelength control signals are respectively output to respective drive units in the variable wavelength transmission units. These tables are also incorporated in the read-only memory (ROM). The contents of the wavelength control tables I to VIII will be also described later.
A clock generating unit 701 generates a predetermined clock signal, supplies it to the buffer control unit and further frequency-demultiplies it and outputs the frequency-demultiplied one to the ROM counter.
The contents of the above wavelength control tables I to VIII show the wavelength transition of the optical signals transmitted from the variable wavelength transmission units, and are set as shown in Table 1, for example.
Further, the offset values of the above buffer control tables I to VIII are set as illustrated in Table 2.
Those sixteen tables are all read out synchronously by the ROM counter 702. Thus, the transmission wavelengths of the respective tunable laser diodes (TLDs) are shifted and circulated in the order of xcex1, xcex3, xcex5, xcex7, xcex8, xcex6, xcex4, xcex2 and xcex1, and the offset value for reading the memory regions in the dual port memory of the buffer connected to each tunable laser diode (TLD) is circulated in the order A1, A3, A5, A7, A8, A6, A4, A2 and A1, which is synchronous with the transition of the variable wavelength of each variable wavelength transmission unit. Therefore, in accordance with the wavelength control tables and the buffer control tables, the packets in the memory regions corresponding to the shifted and circulated wavelength of variable wavelength transmission units are converted into optical signals at transmission wavelengths of the respective variable wavelength transmission units at respective times and output therefrom. Further, circulations of the transmission wavelengths of the respective tunable laser diodes (TLDs) are shifted from each other in phase such that the plural tunable laser diodes (TLDs) do not perform transmissions at the same wavelength at each time. The transmission wavelengths of the variable wavelength transmission units are thus controlled by the above-discussed wavelength control tables I to VIII.
[Operation of This Example]
Now, description will be made as to the transmission control method of this network system with reference to FIGS. 3, 4, 5, 6, 7, 14A and 14B and Tables 1 and 2.
[Transmitted Object of This Example]
To describe the transmission control method, an example of the packet transmission will be described referring to a case where a transmitting terminal equipment is the terminal equipment connected to the sub-transmission line I 1405 of the node device I 301 and an addressed terminal equipment is the terminal equipment II 1414 connected to the sub-transmission II 1406 of the node device II 302. Hereinafter, the packet to be transmitted is called a packet A. Also, the same elements in different node devices are represented by common reference numerals used in FIGS. 4, 5, 6 and 7 for convenience"" sake.
[Operation in the Transmitting Node Device]
Initially, the communication operation of the terminal equipment I 1413 connected to the node device I 301 will be described. The transmitting terminal equipment I 1413 connected to the sub-transmission line I 1405 of the node device I 301 composes the packet A of both a data portion to be transmitted to the receiving terminal equipment II 1414 connected to the node device II 302 through the sub-transmission line II 1406, and an address portion to exhibit the address of the receiving terminal equipment II 1414, and the packet A is output to the separation-insertion unit I 133 of the node device I 301 through the sub-transmission line I 1405.
The separation-insertion unit I 133 of the node device I 301 finds a break in the packet stream received by the fixed wavelength reception unit I 117, inserts into this break the packet A input through the sub-transmission line I 1405 and outputs it to the buffer I 145. In the buffer I 145, the decoder 401 reads the address portion of the input packet A. In this case, since the destination for receiving the packet A is the terminal equipment II 1414 connected to the adjacent node device II 302, the decoder 401 sets such that the demultiplexer 404 outputs to the dual port memory 405 and outputs the predetermined writing start address value A2 of the packet A to the writing address counter 402. The writing address counter 402 thus starts with the writing start address value of the packet A and outputs discrimination signals of the memory regions, in which the packets are to be written, to the dual port memory in order. The packet A is stored in the memory region II in the dual port memory 405 because the packet A is to be transmitted to the terminal equipment II 1414 connected to the node device II 302. Since the terminal equipment II 1414 is connected to the separation-insertion unit II 137 in the node device II 302, the packet A needs to be converted into the optical signal of the wavelength xcex2 and input into the fixed wavelength reception unit II 121 connected to the separation-insertion unit II 137 in the node device II 302, so that the packet can reach the terminal equipment II 1414. The packet stored in the memory region II of the dual port memory 405 is read only when the transmission wavelength of the variable wavelength transmission unit is controlled to be set to the wavelength xcex2. As a result, the packet A is converted into the optical signal at the wavelength xcex2 and output to the node device II 302, when the transmission wavelength of the variable wavelength transmission unit is xcex2.
However, when the destination address of the input packet read by the decoder 401 in each node device is not the address of the terminal equipment connected to the adjacent node device, the decoder 401 sets the output of the demultiplexer 404 to be connected to the FIFO 406 and the received packet is stored in the FIFO 406.
The ROM counter 702 of the wavelength control unit 165 in the node device I 301 simultaneously outputs the reading address value to the wavelength control tables I to VIII and the buffer control tables I to VIII, on the basis of the clock signal of the clock 701. In accordance with the address value, the contents of the wavelength control tables and the buffer control tables are output to the respective variable wavelength transmission units and buffers. For example, when the reading address value 6 is output from the ROM counter 702 to the respective wavelength control tables and buffer control tables, the contents to be read is as follows, as shown in Table 1: The control signal corresponding to the wavelength xcex4 is read from the wavelength control table I, and the control signals corresponding to the wavelength xcex2, the wavelength xcex1, the wavelength xcex3, the wavelength xcex5, the wavelength xcex7, the wavelength xcex8 and the wavelength xcex6 are respectively read from the wavelength control tables II, III, IV, V, VI, VII and VIII. Those control signals are respectively input into the variable wavelength transmission units connected to the respective wavelength control tables. Each variable wavelength transmission unit transmits the optical signal at a predetermined wavelength on the basis of the control signal.
Further, the reading address value 6 is also output from the ROM counter 702 in the wavelength control unit 165 to the respective buffer control tables in the buffer control unit 164. The contents of the buffer control tables I to VIII are read in accordance with the address value. The contents to be read is as follows, as shown in Table 2: The offset value A4 corresponding to the memory region IV is read from the buffer control table I, and the offset values A2, A1, A3, A5, A7, A8 and A6 corresponding to the memory regions II, I, III, V, VII, VIII and VI are respectively read from the buffer control tables II, III, IV, V, VI, VII and VIII. Those offset values are respectively input into the reading address counters 403 of the respective buffers I to VIII.
Further, on the basis of the clock signal output from the wavelength control unit, the reading control unit 609 in the buffer control unit 164 outputs to the selector 407 a control signal of reading permission of the dual port memory and reading prohibition of the FIFO, during a dual port memory reading period Td. Then, the reading control unit 609 outputs to the selector 407 a control signal of reading permission of the FIFO and reading prohibition of the dual port memory, during a predetermined FIFO reading period Tf. Those outputs are changed over alternately. Thus, the input terminal of the selector 407 is selectively connected to the FIFO 406 or the dual port memory 405. The reading control unit 609 controls output time periods of respective reading permission control signals such that the total time period of the reading period Td of the dual port memory and the reading period Tf of the FIFO coincides with a period during which the variable wavelength transmission unit transmits the optical signal at a wavelength.
During the reading period Td of the dual port memory, the reading address counter 403 in the buffer I 145 performs loading thereinto the offset value A4 from the buffer control table I 601, and generates an address for reading the packet written in the memory region IV by performing an increment of the counter in due order to supply it to the dual port memory 405. The reading address permits the dual port memory 405 to read out and output the packet to the variable wavelength transmission unit I 129. Since the packet A is not stored in the memory region IV in the buffer I 145, the packet A is not output to the variable wavelength transmission unit I 129.
During the reading period Tf of the FIFO, the reading control unit 609 in the buffer control unit 164 outputs to the selector 407 the control signal of reading permission of the FIFO and reading prohibition of the dual port memory, and the selector 407 outputs the packet stored in the FIFO 406 to the variable wavelength transmission unit I 129.
Then, the ROM counter 702 of the wavelength control unit 165 counts the clock signal of the clock 701, and simultaneously outputs the reading address value 7 to the wavelength control tables I to VII and the buffer control tables I to VII. The contents to be read from the wavelength control table I 703 is the control signal corresponding to the wavelength xcex2 as shown in Table 1. The control signal corresponding to the wavelength xcex2 is input into the variable wavelength transmission unit I 129 connected to the wavelength control table I 703. The variable wavelength transmission unit I 129 transmits the optical signal of the wavelength xcex2 in accordance with the control signal.
Further, the reading address value 7 is also output from the ROM counter 702 in the wavelength control unit 165 to the respective buffer control tables I to VIII in the buffer control unit 164. The contents of the buffer control tables I to VIII are read in accordance with the address value. The contents to be read from the buffer control table I is the offset value A2 corresponding to the memory region II as shown in Table 2.
In synchronization with the output of the reading address value to each table, on the basis of the clock signal output from the wavelength control unit, the reading control unit 609 in the buffer control unit 150 outputs to the selector 407 the control signal of reading permission of the dual port memory and reading prohibition of the FIFO. During the reading period Td of the dual port memory, the reading address counter 403 in the buffer I 145 performs loading thereinto the offset value A2 from the buffer control table I 601, and generates the address for reading the packet A written in the memory region II by performing an increment of the counter in due order to supply it to the dual port memory 405. The reading address permits the dual port memory 405 to read out and output the packet A to the variable wavelength transmission unit I 129. The packet A is converted into the optical signal of the wavelength xcex2 by the variable wavelength transmission unit I 129, and output to the coupler 1403. The respective variable wavelength transmission units II to VIII convert the packets output from the buffers II to VIII into optical signals of predetermined wavelengths on the basis of the wavelength control signal from the wavelength control unit 151, and output them to the coupler 1403. As described above, wavelengths of the optical signals transmitted from the variable wavelength transmission units II 125, III 130, IV 126, V 131, VI 127, VII 132 and VIII 128 at this time are xcex1, xcex3, xcex5, xcex7, xcex8, xcex6 and xcex4. Thus, the wavelengths of the optical signals emitted from the eight variable wavelength transmission units are made different from each other by the control of the wavelength control unit 151, so that those are multiplexed by the coupler 1403 without being affected by each other. The optical signals of all the wavelengths are thus input into the optical fiber 1404 and transmitted to the adjacent node device downstream of this node device.
The packet A transmitted through the optical fiber 1404 is only received by the fixed wavelength reception unit II 121 in the node device II 302.
The received packet A is separated from the packet to be transmitted to the buffer II 141, by the separation-insertion unit II 137, and transmitted to the addressed terminal equipment II 1414.
The above-discussed example, however, has the following technical disadvantage.
In the network system and the transmission control method of the above example, where the transmitting terminal equipment and the addressed receiving terminal equipment are connected to different separation-insertion units in the same node device, for example, the packet output from the variable wavelength transmission unit is relayed and transmitted by all the node devices, arranged in a loop form, but this node device concerned, received by the fixed wavelength reception unit which outputs the packet to the separation-insertion unit connected to the addressed terminal equipment, output to the sub-transmission line through the separation-insertion unit and received by the addressed terminal equipment. Thus, where the transmitting terminal equipment and the addressed receiving terminal equipment are connected to the different separation-insertion units in the same node device, the transmitted packet circulates through the network and reaches the addressed terminal equipment.
In view of the above-discussed example, the present invention features interactive or bi-directional transmission of a signal. In the present invention, not only sequential transmission of a signal in a predetermined direction but also reverse transmission of a signal can be executed. In the sequential transmission, the signal is transmitted from a first node device to a second node device and from the second node device to a third node device, for example. In the reverse transmission, the signal is transmitted from the second node device to the first node device, for example.
A transmission control method of the present invention is as follows:
The transmission control method to be performed in a network system, which has a plurality of node devices and in which a signal is interactively transmitted between the node devices, includes a step of temporarily storing a signal to be output, in a first node device which is one of the plural node devices, and a step of outputting the temporarily-stored signal in the first node device selectively to a second node device, which is adjacent to the first node device, through a first channel, or to a second channel which is used when the second node device outputs a signal to the first node device. In the outputting step, the first node device is controlled such that when the second node device is not transmitting a signal to the second channel, the first node device can output the signal to the second channel to which no signal is output.
In this transmission control method, the first node device can handle a signal, which is output to the first channel in a first direction and reaches the second node device, and a signal which is output to the second channel in a second direction from the second node device and input into the first node device. Further, since the first node device can output a signal to the second channel such that this signal does not collide with a signal input from the second node device, the first node device can transmit a signal without passing the all the node devices on the network even when the first node device outputs a signal to a sub-transmission line connected to this node device concerned. Further, the transmission direction can be reversed by outputting a signal using the second channel.
Various configurations can be adopted as the channel. For example, there are a configuration which uses light of different wavelengths for discriminating the different channels from each other and a configuration which uses different transmission lines. This can be readily understood by considering that whether the channels are the same or not is decided by judging whether the channels are input into the same device or not. For example, the channels are decided to be the same when the channels are input from different transmission units to the same reception unit, and the collision between signals can be prevented by not outputting the signals thereto at the same time.
The output of the signal is preferably performed by changing the channel connected to a storing unit which temporarily stores the signal to be output and reading the signal from the storing unit when the storing unit is connected to a channel to which the signal is to be output. Specifically, when the alteration of the channel connected to the storing unit is executed pursuant to a pattern, there is no need to decide the channel, to which a signal is to be output, on the basis of the address of the signal and to change the connected channel pursuant to the decision, so that a load at the time of the signal output can be notably lightened.
Various patterns can be used as the pattern. For example, there are a pattern which sets such that the first channel and the second channel can be evenly selected and a pattern which sets such that time used by one of the first channel and the second channel is set longer than time used by the other. Specifically, in a network in which a need of the reversal is small, time used by the first channel can be set longer than time used by the second channel.
On the other hand, in the second node device, the following is performed:
A signal to be output is temporarily stored in the second node device; and
A signal is output to the first node device from the second node device using the second channel while the first node device is selecting the first channel pursuant to the pattern.
At this time, also in the second node device, when the output of the signal is performed by changing the channel connected to a storing unit, which temporarily stores the signal to be output, pursuant to the pattern and reading the signal from the storing unit when the storing unit is connected to a channel to which the signal is to be output, the patterns used by the first node device and the second node device have the same time length and those patterns are set such that different channels can be selected at the same time, a load of the control can be reduced, similar to the first node device. Here, in the first and second node devices, it is preferable that the timing of the channel alteration is adjusted and that the pattern in the first node device is used at the same timing as the pattern in the second node device.
An example of a way for deciding the pattern will be described. Numbers of the first channel and the second channel are the same, and the pattern in the first node device is a pattern in which after a first channel selection pattern for selecting the first channel is selected n1 (an integer) times, a second channel selection pattern for selecting the second channel is selected n2 (an integer) times.
Here, the collision between the signals can be prevented by the following operation of the second node device.
A signal to be output is temporarily stored in the second node device; and
A signal is output to the first node device from the second node device using the second channel while the first node device is selecting the first channel pursuant to the pattern.
Furthermore, the pattern used in the second node device can be decided as follows:
The second node device outputs the temporarily-stored signal in the second node device selectively to the first node device through the second channel, or to the first channel which is used when the first node device outputs the signal to the second node device. Here, the output of the signal through the selected channel is performed by changing the channel connected to the storing unit which temporarily stores the signal to be output in the second node device and reading the signal from the storing unit when the storing unit, is connected to the channel to which the signal is to be output. The pattern in the second node device is a pattern in which after the second channel selection pattern for selecting the second channel is selected n1 (an integer) times, the first channel selection pattern for selecting the first channel is selected n2 (an integer) times. In the first and second node devices, the pattern in the first node device is used with the same timing as the pattern in the second node device.
Further, another way for deciding the pattern may be the following method:
Further, another way for deciding the pattern may be the following method:
The number of the first channels is N1 and the number of the second channels is N2 (N1 greater than N2), and the pattern in the first node device is a pattern in which after the first channel selection pattern for selecting the first channel is selected n1 times, the second channel is selected N2xc2x7CM2/N1 times among nn2 second channel selection pattern for selecting the second channel, where the larger of common multiples between N1 and N2 is CM1, the smaller thereof is CM2, a value obtained by dividing CM1 by N1 is n1, a value obtained by dividing CM1 by N2 is n2, a value obtained by dividing CM2 by N1 is nn1 and a value obtained by dividing CM2 by N2 is nn2.
Here, similar to the above, the collision between the signals can be readily prevented by the following operation of the second node device.
A signal to be output is temporarily stored in the second node device; and
A signal is output to the first node device from the second node device using the second channel while the first node device is selecting the first channel pursuant to the pattern.
Furthermore, the pattern used in the second node device can also be decided as follows:
The second node device outputs the temporarily-stored signal in the second node device selectively to the first node device through the second channel, or to the first channel which is used when the first node device outputs the signal to the second node device. Here, the output of the signal through the selected channel is performed by changing the channel connected to the storing unit which temporarily stores the signal to be output in the second node device and reading the signal from the storing unit when the storing unit is connected to the channel to which the signal is to be output. The pattern in the second node device is a pattern in which after the second channel selection pattern for selecting the second channel is selected n2 times, the first channel selection pattern for selecting the first channel is selected nn1 times. In the first and second node devices, the pattern in the first node device is used with the same timing as the pattern in the second node device.
Further, when the pattern is to be set, the pattern can also be decided such that a ratio in the pattern between time, during which the first channel is selected, and time, during which the second channel is selected, is approximately the same as a ratio between time, which is needed to output the signal to be output to the first channel, and time, which is needed to output the signal to be output to the second channel.
Furthermore, when the pattern is altered pursuant to the situation, the pattern can be set according to the traffic of the network system.
An example of the pattern alteration is as follows:
The pattern is altered such that the first ratio in the pattern between time, during which the first channel is selected, and time, during which the second channel is selected, becomes closer to the second ratio between time, which is needed to output the signal to be output to the first channel, and time, which is needed to output the signal to be output to the second channel. An example of the signal used in the present invention is packet signals which respectively have address data. The packet signal may be a signal having a fixed length, such as a cell in ATM communications, or a signal having a variable length whose length is not fixed. For example, where the fixed-length signal is treated, the above second ratio between time, which is needed to output the signal to be output to the first channel, and time, which is needed to output the signal to be output to the second channel, can be known by monitoring the number of the signals to be output through the first channel and the number of signals to be output through the second channel and obtaining a ratio between those numbers. Therefore, the pattern may be altered such that the above first ratio approaches the above second ratio. The signals may be monitored by this node device concerned or another node device.
Such pattern alteration may be performed as follows: The pattern is composed of the first channel selection pattern for selecting the first channel and the second channel selection pattern for selecting the second channel, and the pattern is altered by changing the number of the first channel selection patterns and the number of the second channel selection patterns. The reason therefor is that the pattern can be altered by the combination of sub-patterns without making again the entire pattern from the beginning each time the alteration is desired.
Further, in the first node device, when the signals are input thereinto from another node device through a plurality of channels, the storing unit stores the signals in a divided form per each input channel and the storing unit outputs the respective signals from its different output portions, the channels of the signals transmitted from another node device can be interchanged in the first node device. A specific structure of the storing unit may be a structure in which buffers are respectively provided for the input channels. Outputs from the respective buffers can be considered as outputs from the respective different output portions.
Specific constructions may be as follows: The first node device includes variable channel transmission units corresponding to the respective output portions, and the channels connected to the storing unit are altered by changing the transmission channels of the respective variable channel transmission units. The first node device includes a connection alteration unit provided with input terminals corresponding to the respective output portions and output terminals corresponding to the respective channels, and the channels connected to the storing unit are altered by changing the relationship between the input terminals and the output terminals of the connection alteration unit.
Furthermore, where the following control is performed in addition to the above-discussed control, communication can also be performed with a third node device which is further another node device adjacent to the first node device.
The signals are stored in the first node device with the following signals being discriminated from each other: A first kind of signals is a signal which is output selectively to the adjacent second node device through the first channel, or to the second channel which is used when the second node device outputs the signal to the first node device, and a second kind of signals is a signal which is output selectively to the adjacent third node device through a third channel, or to a fourth channel which is used when the third node device outputs the signal to the first node device. Here, the first node device is controlled such that when the third node device is not transmitting the signal to the fourth channel, the first node device can output the signal to be output to the fourth channel, out of the signals which are selectively output through the third channel or the fourth channel, to the fourth channel to which no signal is output.
When such control is performed, the above-discussed controls of the first node device and the second node device can also be applied to controls of the first node device and the third node device. As will be described in the following embodiments, when the structure of a loop-type network is adopted, the first and fourth channels serve as channels for transmitting in a first direction and the second and third channels serve as channels for transmitting in a direction opposite to the first direction.
In the present invention, the first node device outputs the signal to be output to the sub-transmission line connected to this node device, out of the signals stored in the first storing unit, to the second channel, and outputs the signal to be output to the sub-transmission line connected to this node device, out of the signals stored in the second storing unit, to the fourth channel. Thus, the signal to be separated from the second channel to the addressed sub-transmission line, out of the signals stored in the first storing unit, is separated and reaches the addressed destination after output through the second channel, while the signal to be separated from the first channel to the addressed sub-transmission line, out of the signals stored in the first storing unit, is once again temporarily stored in the second storing unit after output through the second channel and output through the first channel to reach the addressed destination. The signals from the second storing unit are also dealt with in the same manner.
Further, in order to prevent unnecessary reversal of the transmission, the first node device only needs to be controlled such that it does not output the signal, whose output channel need not be designated, out of the temporarily-stored signals, when the signal can be output to the second and fourth channels.
Further, where the first, second and third node devices are arranged, the first node device only needs to be controlled such that the signal output to the fourth channel is input into the first storing unit of the first node device and that the signal output to the second channel is input into the second storing unit of the first node device.
Further, the node device is preferably constructed such that it is connected to the terminal equipment and the like through the sub-transmission line and that the signal to be output to the sub-transmission line connected to this node device, out of the input signals, is separated from other signals and output to this sub-transmission line.
Further, when the storing unit is constructed such that it stores the signals in a divided form for different channels to which those signals are to be output, control for reading the signals is facilitated and speedy reading can be attained.
Further, in the node device, since all the signals need not be transmitted with their channels being designated, it is preferable that the storing unit stores the signal, whose output channel is to be designated, and the signal, whose output channel is not to be designated, in a separate form from each other.
Furthermore, a network system of the present invention is constructed in the following manner.
The network system, which includes a plurality of node devices and performs an interactive or bi-directional transmission of a signal between the node devices, includes a first node device which is a node device of the plural node devices and have the following units. Those are a storing unit for temporarily storing the signal to be output, and a connection unit for connecting the storing unit to a first channel for outputting to an adjacent second node device or a second channel for outputting from the second node device to the first node device. The connection unit connects the storing unit to the second channel, to which no signal is output, when the second node device is not outputting the signal to the second channel.
The present invention further includes network systems for performing the above-discussed transmission controls.
In particular, as a specific structure, the transmission unit for performing the optical transmission may be a structure using a tunable laser and devices for combining or multiplexing, dividing and demultiplexing the optical signal are used. Further, another structure for altering channels may be a structure using a switch.